1. Field of the Invention
The present invention generally relates to implantable medical devices, and more specifically, relates to chronically implantable devices for determination of the posture of a patient.
2. Description of the Prior Art
Posture detection devices have been known in the art for some time. Often these are implanted and used for control of the pacing rate of an artificial cardiac pacer. The typical method is through the use of gravity using a mercury switch, for example. The gravity switch method, of course, provides only a binary or two state output. Either the switch is open or it is closed.
Intravascular pressure sensors are also known in the art. U.S. Pat. No. 4,407,296 issued to Anderson teaches a chronically implantable pressure transducer suitable for use in the cardiovascular system. A pressure transducer with an improved electronic circuit is taught in U.S. Pat. No. 4,432,372, issued to Monroe. A further improved pressure transducer is taught in U.S. Pat. No. 4,485,813, issued to Anderson, et al. These pressure sensors have been directed to the control of artificial cardiac pacers using algorithms which convert measurements of pressure or change of pressure into pacing rate.
U.S. Reissue Pat. No. 30,372, issued to Mirowski, et al. teaches control of an implantable defibrillator using an intravascular pressure sensor. None of these references teaches the use of differential pressure measurement to determine the posture of the patient.